Jerry (n.)

World War I British Army slang for "a German; the Germans," 1919, probably an alteration of German based on the male nickname Jerry, popular form of Jeremy. But it also is said to be from the shape of the German helmet, which was thought to resemble a jerry, British slang for "chamber pot, toilet" (1850), this being probably an abbreviation of jeroboam, which is attested in this sense from 1827. Compare jerry-hat "round felt hat" (1841).